Gas turbines are widely used in industrial and power generation operations. A gas turbine generally includes, in serial flow order, a compressor, a combustion section and a turbine. The combustion section may include multiple combustors annularly arranged around an outer casing. In operation, a working fluid such as ambient air is progressively compressed as it flows through the compressor. A portion of the compressed working fluid is routed from the compressor to each of the combustors where it is mixed with a fuel and burned in a combustion zone to produce combustion gases. The combustion gases are routed through the turbine along a hot gas path where thermal and/or kinetic energy is extracted from the combustion gases via turbine rotors blades coupled to a rotor shaft, thus causing the rotor shaft to rotate and produce work and/or thrust.
Some combustion systems utilize a plurality of dual fuel premix type fuel nozzles. A dual fuel type fuel nozzle may be configured to provide a liquid fuel only, a gaseous fuel only or may be configured to provide both a liquid fuel and a gaseous fuel. This flexibility is typically accomplished by mounting or inserting an appropriate cartridge type through a center body portion of the fuel nozzle. For example, a cartridge may be configured to provide liquid fuel, gaseous fuel and/or may be configured to provide a purge medium such as compressed air through the center body. For gas turbines which have no provision to run liquid fuel and are as such “gas only”, gas only cartridges are placed in the center body of the fuel nozzles. The gas only cartridges must be cooled as well as purged so that the hot combustion gases are not allowed into the cartridge cavity.
In particular combustors, at least one of the fuel nozzles may include a premix pilot tip or nozzle. During particular combustion operation modes, the premix pilot nozzle may deliver a premixed fuel and air mixture to the combustion zone to produce a pilot flame. The pilot flame is generally used to ensure flame stability as the combustor is operated in certain modes and/or when the combustor transitions between various modes of operation. Unstable flames have a high susceptibility to undesirable fluctuations in heat release. The base of the pilot flame typically resides adjacent to or just downstream from an exit face of the premix pilot nozzle. As a result, the exit face is exposed to extremely high temperatures.
The premix pilot nozzle is typically disposed at a distal end of the center body upstream from the combustion zone. In certain configurations, a portion of the gas only cartridge extends through the premix pilot nozzle. A tip portion of the gas only cartridge and a tip portion the premixed pilot nozzle may be substantially planar along their exit faces. As a result, purge air flowing from the cartridge may negatively impact pilot flame stability.
Known cartridges may create strong jets of air at their exit face which may cause pilot flame instability. In addition, the premixed pilot nozzles may create a high temperature environment at the planar faces of the cartridge and the premixed pilot nozzle. Accordingly, an improved fuel nozzle that reduces flame instability while providing cooling to the exit faces of the premix pilot nozzle and/or the gas only cartridge would be useful in the art.